Technical Field
The present invention relates to an angle detection device and an angle detection method.
Background Art
To detect the rotation angle of a rotating body, a method and a device are known in which a magnetic sensor is fixed closely to a rotating body to which a permanent magnet is provided and relatively rotated with the rotating body to detect the rotation angle thereof based on the output waveform of the magnetic sensor that changes with the rotation.
However, the detection accuracy by these tends to deteriorate unless care is taken about selection based on the sensitivity of a magnetic sensor, improvement of accuracy of magnetization of a permanent magnet, highly precise arrangement of a magnet sensor, etc.
In attempts to prevent such deterioration, a digital angle measuring system is known which includes a control circuit to detect an amplitude of a magnetic sensor output signal and calculate an amplification ratio to correct the detected amplitude to a desired value, an AD converter to convert the magnetic sensor output signal to digital data, and a variable amplifier using an operational amplifier to amplify the output signal of the magnetic sensor based on the amplification ratio to control the amplitude of the amplified output signal of the magnetic sensor to be input to the AD converter.
However, the variable amplifier of this digital angle measuring system is configured using an operational amplifier, it is necessary to cancel input offset of the operational amplifier, which degrades angle detection precision. That is, if a gain is multiplied with a sinusoidal signal by an amplifier, offset of the amplifier is added to the sine waveform, which makes another factor of error.
For this reason, in this digital angle measuring system, a chopper switch is arranged just before the variable amplifier and, a chopper demodulator, just after the variable amplifier. This arrangement increases cost.